1 | /*
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2 | * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
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3 | *
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4 | * Licensed under the OpenSSL license (the "License"). You may not use
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5 | * this file except in compliance with the License. You can obtain a copy
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6 | * in the file LICENSE in the source distribution or at
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7 | * https://www.openssl.org/source/license.html
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8 | */
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9 |
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10 | /*
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11 | * NB: These functions have been upgraded - the previous prototypes are in
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12 | * dh_depr.c as wrappers to these ones. - Geoff
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13 | */
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14 |
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15 | #include <stdio.h>
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16 | #include "internal/cryptlib.h"
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17 | #include <openssl/bn.h>
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18 | #include "dh_locl.h"
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19 |
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20 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
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21 | BN_GENCB *cb);
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22 |
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23 | int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
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24 | BN_GENCB *cb)
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25 | {
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26 | if (ret->meth->generate_params)
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27 | return ret->meth->generate_params(ret, prime_len, generator, cb);
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28 | return dh_builtin_genparams(ret, prime_len, generator, cb);
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29 | }
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30 |
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31 | /*-
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32 | * We generate DH parameters as follows
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33 | * find a prime q which is prime_len/2 bits long.
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34 | * p=(2*q)+1 or (p-1)/2 = q
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35 | * For this case, g is a generator if
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36 | * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
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37 | * Since the factors of p-1 are q and 2, we just need to check
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38 | * g^2 mod p != 1 and g^q mod p != 1.
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39 | *
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40 | * Having said all that,
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41 | * there is another special case method for the generators 2, 3 and 5.
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42 | * for 2, p mod 24 == 11
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43 | * for 3, p mod 12 == 5 <<<<< does not work for safe primes.
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44 | * for 5, p mod 10 == 3 or 7
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45 | *
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46 | * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
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47 | * special generators and for answering some of my questions.
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48 | *
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49 | * I've implemented the second simple method :-).
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50 | * Since DH should be using a safe prime (both p and q are prime),
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51 | * this generator function can take a very very long time to run.
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52 | */
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53 | /*
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54 | * Actually there is no reason to insist that 'generator' be a generator.
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55 | * It's just as OK (and in some sense better) to use a generator of the
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56 | * order-q subgroup.
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57 | */
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58 | static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
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59 | BN_GENCB *cb)
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60 | {
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61 | BIGNUM *t1, *t2;
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62 | int g, ok = -1;
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63 | BN_CTX *ctx = NULL;
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64 |
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65 | ctx = BN_CTX_new();
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66 | if (ctx == NULL)
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67 | goto err;
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68 | BN_CTX_start(ctx);
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69 | t1 = BN_CTX_get(ctx);
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70 | t2 = BN_CTX_get(ctx);
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71 | if (t1 == NULL || t2 == NULL)
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72 | goto err;
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73 |
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74 | /* Make sure 'ret' has the necessary elements */
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75 | if (!ret->p && ((ret->p = BN_new()) == NULL))
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76 | goto err;
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77 | if (!ret->g && ((ret->g = BN_new()) == NULL))
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78 | goto err;
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79 |
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80 | if (generator <= 1) {
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81 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
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82 | goto err;
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83 | }
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84 | if (generator == DH_GENERATOR_2) {
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85 | if (!BN_set_word(t1, 24))
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86 | goto err;
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87 | if (!BN_set_word(t2, 11))
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88 | goto err;
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89 | g = 2;
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90 | } else if (generator == DH_GENERATOR_5) {
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91 | if (!BN_set_word(t1, 10))
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92 | goto err;
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93 | if (!BN_set_word(t2, 3))
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94 | goto err;
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95 | /*
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96 | * BN_set_word(t3,7); just have to miss out on these ones :-(
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97 | */
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98 | g = 5;
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99 | } else {
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100 | /*
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101 | * in the general case, don't worry if 'generator' is a generator or
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102 | * not: since we are using safe primes, it will generate either an
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103 | * order-q or an order-2q group, which both is OK
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104 | */
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105 | if (!BN_set_word(t1, 2))
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106 | goto err;
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107 | if (!BN_set_word(t2, 1))
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108 | goto err;
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109 | g = generator;
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110 | }
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111 |
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112 | if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
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113 | goto err;
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114 | if (!BN_GENCB_call(cb, 3, 0))
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115 | goto err;
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116 | if (!BN_set_word(ret->g, g))
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117 | goto err;
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118 | ok = 1;
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119 | err:
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120 | if (ok == -1) {
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121 | DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
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122 | ok = 0;
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123 | }
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124 |
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125 | if (ctx != NULL) {
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126 | BN_CTX_end(ctx);
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127 | BN_CTX_free(ctx);
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128 | }
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129 | return ok;
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130 | }
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